In 2008, a ruling by the Federal Communications Commission (FCC) paved the way for commercial wireless networking products to operate over white spaces. White spaces are the vacant channels in the VHF and UHF frequency spectra. Unlike the frequency spectra available for mature wireless networking protocols (for example, Wi-Fi networking), the spectrum available for white space networks is well-suited to covering a relatively large area. For example, a white space network could be employed in a corporate or university campus setting to allow a large number of users to access a common network across several buildings over an area of a few hundred square feet to one or more square miles.
The FCC ruling that authorized the creation of white space wireless devices also established some rules that could make the implementation of white space networks in urban campus environments more difficult. For example, a requirement of the FCC ruling is for new white space wireless devices to avoid interference with primary users or incumbent devices. Primary users and incumbent devices include TV transmitters and wireless microphones. Moreover, new white space devices are not allowed to transmit on channels that are being used by primary users (which, for example, in the UHF TV bands are television stations and licensed wireless microphones), even if the primary user begins broadcasting after the white space device.
In many existing wireless communication protocols (such as the Wi-Fi protocol), a base station and all connected client devices must be on the same channel in order to allow for the protocol to work correctly. If white space network devices followed the same strategy (i.e., all client-devices connected to the same base station must be on the same channel), a wireless base station that is communicating with a number of wireless clients would need to disconnect from all connected client devices or change channels to an available channel if a primary user such as a wireless microphone is identified on the channel being used by the wireless base station. This rule would have a significant detrimental impact on the throughput of white space networks. Moreover, even if only one of the associated clients sees the channel as becoming unavailable, then either this client would become disconnected, or alternatively, the base station and all other associated clients would need to switch to a new channel that is available at all clients as well as the base station. This is problematic because there may not be such a channel that is available on all associated client devices as well as at the base station. Even if such a commonly available channel exists, having all clients and the base station switch whenever the channel becomes unavailable at a single client could incur significant overhead. In urban environments, it is likely that such a scenario (i.e., only one or few clients sees a channel as unavailable) occurs frequently due to the presence of wireless microphones.